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HelicopterEngines Plugs Mufflers Fuel › I fried my OS .91HZ-PS - help!
11-29-2011 03:30 AM  5 years agoPost 1
ticedoff8

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Morgan Hill, CA. USA

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Last weekend, I fried the piston / ring and scratched the sleeve on my OS .91HZ-PS.

I have about 50 flights on this engine - average about 10min per flight. Just cruising around - no 3D. Raptor 90.

In the past 50 flights, I have had occasional / intermittent issues where the engine will "go lean" in the middle of a flight. The amount of smoke goes from "normal" to just a wisp, the engine starts to sound fast and the gov doesn't seem to keep it under control.
In the past, I would land, and the engine wouldn't idle down to "normal" - it was still lean and it would be running at a much faster idle. I clamp the fuel line to stop the engine, and you could smell the engine was hot.
The next time I started, everything would be normal - good power, good smoke trail and all is right with the flight. I would run a full tank and part of the header tank with no problems.
I could do 5 or 10 or 2 more flights with everything normal - then in the middle of a flight - trouble - too lean.

Last Friday, it happened again. But I was to high and in the wrong position to auto - I ended up running the engine until about 5' from landing - then poof - dead. Auto from 5'.

One of the guys at the field said the .91HZ-PS has a bad pump / regulator - it is a bad design and failure prone.
I've searched this section, and I can find only 1 reference to a bad HZ-PS.
I found some that reference the SZ-PS - but the HZ-PS & the SZ-PS use different pumps.

I guess my question is: What would cause an intermittent lean condition?

Is it a bad regulator / debris in the regulator?
Is is a bad pump?
Debris in the fuel filter?

I really can not find any garbage in the fuel system - but it may be too small for me to see.

I have $180 worth of parts on order to repair the engine. I really don't want to do this again.

A guy at the field is letting me borrow one of his "spare" -R regulator / carbs (he bought a couple of the conversion kits).
Until I figure out what went wrong with the -PS setup, I know I don't trust it.

Has anyone had bad experiences with the OS .91 HZ-PS system?

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11-29-2011 04:02 AM  5 years agoPost 2
dchekas

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Farmington, CT

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I can't offer much here other than:

Bert Kammerer, who is sponsored by OS Engines, recommended to people to get either the -R or the Muffler pressure version, and to avoid the pump. For the exact reason you posted above.

I've been running the R for almost 30 gallons, and it's been awesome. If I were you, I'd put my cash into the -R conversion and scrap the pump.

Sorry I couldn't be of more help.

Team Align, Team Futaba, Team Byron Fuels, Team Thunder Power

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11-29-2011 04:24 AM  5 years agoPost 3
TMoore

rrMaster

Cookeville, TN

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Has anyone had bad experiences with the OS .91 HZ-PS system?
At some point, everyone that has a pumped engine will experience what you did. That's just the way it is. The best thing that you can do is to rebuild it, get a one way, pressurize the fuel tank and use the regulated carb. Crankcase pressure is way more reliable than the pump.

TM

Delayed Response Operator Not Engaged

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11-29-2011 07:28 AM  5 years agoPost 4
ticedoff8

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Morgan Hill, CA. USA

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Crankcase pressure is way more reliable than the pump.
and...
get either the -R or the Muffler pressure version, and to avoid the pump
Okay - That confirms it.

And, I understand that the -R conversion would be the best way to go - BUT... I am cheap.
The 91HZ-R Conversion Kit (OSMG4038) is $220. It includes the 61E-R carb.

Is the 61B-P carb (original carb for the .91 HZ-PS) any good? Will it work with a pressurized tank system?

If I get rid of the original pump (PD-08), replace it with a 1-way check valve and continue to use the original HZ-PS carb (61B-P) will it be "close enough" to the 61E-R to be reliable and dependable?

The power output of the .91HZ-PS was well above anything I could imagine - or use.
If the 1-way check valve & the 61B-P carb will work together reliably & dependably, I'd be happy.

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11-30-2011 07:54 AM  5 years agoPost 5
Bugcatcher

rrApprentice

Perth, Australia

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You can't use the check-valve crankcase pressure without the regulated carb as it controls the amount of fuel the carb has to use.

If you don't want to spend the money on the conversion then just discard the pump and use muffler pressure only to the carb instead.

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11-30-2011 05:50 PM  5 years agoPost 6
ticedoff8

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Morgan Hill, CA. USA

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The 61B-P has a regulator built in.
But, it is a slightly different regulator from the one installed on the 61E-R

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11-30-2011 06:41 PM  5 years agoPost 7
rexxigpilot

rrProfessor

Florida

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I'd give it a try. Most RC regulators work on a fairly low input pressure, otherwise fuel lines would not stay on. I don't know exactly what pressure each of the OS regulators use, but you have lots of adjustability for various pressure differences in the high and mid needle settings. I would suspect that the regulator valve/orifice opening in the PS carb's regulator is larger to operate on a lower pressure than with direct crank pressure, but maybe not. Start out very rich an work it in from there. The idle needle is where you may run into a problem. There may not be much adjustability here and the possibly higher (or lower) pressure from the crank may tend to give an excessively rich (or lean) idle that can't be adjusted with the needle.

The R conversion is $220 street price, but through TH just add another item or so and get the $35 to $50 members' discount. My conversion only cost me $170 using that method/mentality. That's $10 less than your engine repair.

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11-30-2011 06:54 PM  5 years agoPost 8
ticedoff8

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Morgan Hill, CA. USA

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rexxigpilot: Thanks for the input.
But the underlaying question is (that has not been answered):
Is the 61B-P any good?

If - as everyone is saying - the pump has an intermittent failure, then the carb / reg should be okay.

As long as I can provide the pressure (1-way check valve, muffler pressure or old-school Perry VP-30 pump), the built-in regulator of the 61B-P should be fine.

Unless the failure is in the regulator (not the pump) - no-one has said that (yet).
Then I burn the engine up again.

I understand; The safest approach is the -R conversion.
Or scrap the OS and change to YS.

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